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Getting in the Zone of Astro Imaging

Posted by Max Corneau   01/05/2008 12:00AM

Getting in the Zone of Astro Imaging
The bottom line up front (BLUF) is that I’m a dedicated fan, possibly even a zealot advocate of Ron Wodaski’s The NewAstro Zone System for Astro Imaging. If you’re a serious imager, this book is a must-have. If you’re not a serious imager, you may not want to invest $100 in a 246-page paperback book published in 2006 that doesn’t come with a CD or DVD.

The Zone System really is about a philosophy of astro imaging. Humorously, I now refer to my book as the “Zen System” as it is a way of thinking about your image data, seeing the data in each channel and operating on it in such a way as to remove the guesswork and take your final image product to the next level. Did you notice that I distinguish image data from the image product. Experienced imagers already understand what I call “pixel math” which is the lowest level of data comprising your images. If you don’t use Photoshop CS or CS2 (or later) to do final image processing, this book is also probably not for you as it relates nearly all the examples to Photoshop tools.

This is not Ron Wodaski’s first book, his first effort, The New CCD Astronomy is also a must-read for the dedicated imager. Perhaps the best description of the two books was posted by Ron himself to his New Astro Yahoo group. “The New CCD Astronomy, which is an encyclopedic coverage of all things related to CCD imaging. There is some material on image processing, and it is introductory and covers both Photoshop and other programs. The Zone System book is more recent, and is focused entirely on detailing a repeatable system for processing astro images using Photoshop.”

When I read this description, the lightbulb went off for me. I thought, it’s all about having a repeatable, clearly understood process. So what about the Zone Process?

Chapter one, simply titled “The Zone System” opens with an immediate description of what the zones are and how to select and operate on them. Following the textual description, Wodaski offers excellent graphical descriptions using imagery and histogram examples depicting the zones. Following a logical progression into the Zone System, chapter two, titled “Photoshop Basics: The Standard Curve” might be more accurately titled The Heart of the Zone System – Curves. Chapter two offers an excellent processing checklist. Since I’m a pilot and space operations officer, I love checklists. I live by checklists. Unfortunately, this checklist appears far too soon in the book and is definitely out of place. It should appear in chapter 4, titled Image Processing Workflow. Another inconsistency relates to the books’ organization. Chapters 1, 2, and 5 offer excellent end of chapter reviews. I wonder why there are no end of chapter reviews in chapters 3, 4, and 6-11.

Chapter three, “Photoshop Processing Tips”, also an outstanding resource, should more accurately be titled, “How to Process Luminance” as it covers this topic quite completely. This chapter provides excellent descriptions of how and why to sharpen bright areas and smooth dim areas as well as how to accomplish interzonal contrast adjustments. Although pictures of dialog boxes on page 41 are redundant to the dialog box pictures on pages 54-57, they are important to understand how and why (quantitatively) adjusting curves affects image data.

Chapter four, “Image Processing Workflow” presents a comprehensive list of steps involved in image processing. Do you see why this is where the checklist presented in chapter 1 should appear? Another organizational note is that on pp 87-88 Wodaski addresses star selection but the next chapter is called “Selecting Stars”. Chapter five, on selecting stars is full of great techniques on how to select and operate on stars to produce the most pleasing results.

Chapters six and seven on controlling color and image cleanup, respectively, go the extra mile to again articulate the hows and whys of image data and manipulation. Especially useful are the explanations of color bias versus color balance and a table on atmospheric extinction. Chapter seven, as do several other chapters, provides links to useful software applications that improve image processing. One of the tools introduced in chapter seven is Russell Croman’s RC Astro plug-in for MaxIm DL. I have used this excellent software application to eliminate unreliable dark frame pixels. Chapter 8 explains various techniques to repair star elongation.

Russell Croman contributed chapters nine and ten to this book and his contributions pertaining to narrow band image acquisition and processing are outstanding. Intentionally or not, in chapter nine (Emission Line Imaging) Croman made me laugh. He explains that one of the advantages of narrow band imaging is that inexpensive achromatic refractors can be used without suffering from the very dreaded chromatic aberration. Ok, so let me get this right, someone is going to spend thousands of dollars on a mount, camera, filter wheel, and narrow band filter set and make the lowest common denominator an inexpensive achromatic refractor? Actually, reflecting more deeply on this point made by Croman I came to realize that all those nights spent visually observing on “Lazarus” the 12” Clark-Saegmueller refractor at the US Naval Observatory could have been spent performing narrowband imaging. Finally, in chapter 10 Croman offers an excellent explanation of why it’s important to save files as IEEE floating point images instant of in 16-bit (integer) format.

Buy this book but be prepared to spend lots of time going back to your old image data and reprocessing in the Zone!

Author's Note: I am in no way affiliated with Ron Wodaski and this review represents my unbiased opinion.